<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.calcdemo.MainActivity"
    tools:ignore="MergeRootFrame" >

    <EditText
        android:id="@+id/et_input"
        android:layout_width="fill_parent"
        android:layout_height="60dip"
        android:background="@drawable/white_bg"
        android:gravity="right|bottom"
        android:text="123.56"
        android:textSize="36sp" />

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="20dp"
        android:orientation="horizontal" 
        android:gravity="center_horizontal">

        <Button
            android:id="@+id/but_clear"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:text="C"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>

        <Button
            android:id="@+id/but_del"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:layout_marginLeft="10dp"
            android:text="Del"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>
        
        <Button
            android:id="@+id/but_divide"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:layout_marginLeft="10dp"
            android:text="/"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>
        
        <Button
            android:id="@+id/but_multply"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:layout_marginLeft="10dp"
            android:text="X"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>
    </LinearLayout>
    
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="20dp"
        android:orientation="horizontal" 
        android:gravity="center_horizontal">

        <Button
            android:id="@+id/but_7"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:text="7"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>

        <Button
            android:id="@+id/but_8"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:layout_marginLeft="10dp"
            android:text="8"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>
        
        <Button
            android:id="@+id/but_9"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:layout_marginLeft="10dp"
            android:text="9"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>
        
        <Button
            android:id="@+id/but_minus"
            android:layout_width="60dp"
            android:layout_height="60dp"
            android:layout_marginLeft="10dp"
            android:text="-"
            android:textSize="20sp" 
            android:gravity="right|bottom"/>
    </LinearLayout>

</LinearLayout>

哪里的问题，怎么两个linearLayout重叠在一起了？效果成了这个样子